Treatment of derivatives of cellulose



Patented Mar. 1, 1 938 f PATENT. OFFICE TREATMENT or DERIVATIVES orCELLULOSE George Schneider, Montclair, N. J., assignor to CelancseCorporation of America, a corpora tion of Delaware No Drawing.

Claims.

This invention relates to derivatives of cellulose and relates moreparticularly to the treatment of organic derivatives of cellulose toreduce their corrosive properties and color and increase.

'5 their clarity characteristics.

An object of my invention is to treat derivatives of cellulose,particularly organic derivatives of cellulose,with bleaching agents toimprove their properties. Another object of my invention is 10 to treatorganic derivatives of cellulose with'solutions of hypoehlorites wherebythe corrosive properties of the organic derivative of cellulose arereduced. Other objects of the inventionwill appear from the followingdetailed description.

lose' acetate, as ordinarily made contain certain colored constituentsor ingredients that tend to impair their usefulness in the making ofplastics, films, filaments and the like, particularly where transparencyand freedom from color are desired.

- For instance, "in spinning a solution of cellulose acetate dissolvedin a volatile solvent by extruding the same through suitable orificesinto an evaporative or precipitating medium, the solutions containingthe celluloseacetate as normally made tend to corrode the jet holes ororifices. If the corroded material remains in the jet hole, there isproduced a filament having a denier below that desired, while if thecorroded material is broken away from the jet hole the jet hole isenlarged, thus producing a filament having a greater denier than thatdesired and of undesirable cross-section. It has been the practiceheretofore to frequently change the spinning jets and to make periodicexamination as to their 5 condition. This interrupts spinning. Moreover,

jet replacements are costly. Furthermore, if improper inspection is madeor the jets are not re-.-

placed frequently there is produced a yarn which is not uniform as todenier, cross-section, etc. This non-uniformity of the yarn reflects inthe fabric produced from the same, sometimes making a second qualityfabric. v

I havefound that if derivatives of cellulose, and particularly organicderivatives of cellulose, are

subjected to the action of a hypoehlorite, chlorine Organic derivativesof cellulose, such as cellu Organic derivatives of cellulose, such ascellu-,

Application November 13, 1935, Serial No. 49,555

water or other bleaching agent prior to being precipitated from thesolution in, which they are formed, a large proportion of the colorimparting and corrosive constituents are either destroyed or areconverted into compounds that tend to produce such objectionableactionto a lesser extent. In accordance with my invention, I preparederivatives of cellulose of reduced corrosive properties and of reducedcolor which derivatives of cellulose are capable of producing productsof greater transparency, by subjecting the primary, secondary or workingsolution of the organic derivative of cellulose to the action of ableaching agent comprising a hypochlorite, chlorine water or otherchlorine liberating material. Chlorine gas may also be employed as thecorro-' sionreducing agent.

While other derivatives of cellulose, such as cellulose nitrate, may betreated in accordance with this invention, I prefer to treat organicderivatives of cellulose, such as organic esters of cellulose andcellulose ethers. Examples of organic esters of cellulose are celluloseacetate, cellulose formate, cellulose propionate and cellulose butyrate,while examples of cellulose ethers are ethyl cellulose, methyl celluloseand benzyl cellulose.

. The organic derivative of cellulose may be formed by any suitablemethod. For instance, cellulose acetate may be formed by treatingcellulose with acetic anhydride in the presence of a catalyst and asuitable diluent or solvent such as acetic acid. The cellulose acetatethus formed may be subjected to a hydrolysis or ripening treatment toproduce the desired solubility characteristics therein. The'ripening orhydrolysis may be performed by allowing the cellulose acetatestilldissolved in the liquors formed during esterii fication to standfor a period of time at suitable temperatures. By this processcellulose-acetate which when formed is soluble in chloroform may be madesoluble in acetone. The other esters of cellulose may be formed in asimilar manner. Forth purpose of describing this invention and in theappended claims, the term. primary solution refers to a solution ofcellulose ester in the solvent produced or added during the esteriflcation of the cellulose. For instance, the primary solution of celluloseacetate as formed in accordance with the above description, is theacetic acid solution of cellulose acetate containing someaceticanhydride and sulphuric acid. Also for the purpose of describingthis invention and in the appended claims, the term secondarysolutionrefers to, a solution of cellulose ester in the solvent producedor'added during the bydroiysls or ripening. Further, for the purpose ofdescribing this invention and in the appended .'claims, the term workingsolution refers to a solution of a cellulose ester, or other organicderivative of cellulose, after it has been precipitated from the primaryor secondary-solution,

I prefer to treat the derivatives of cellulose at the end ofthehydrolysis or ripening step. Thus, the secondary solution ofcellulose acetate may have added theretoa hypochlorite solutionimmediately prior to or during the precipitation of the celluloseacetate from the solution. The precipitating step may be effected byadding to the secondary solution of cellulose acetate a solution of analkali carbonate or an alkali acetate or other alkali salt of a fattyacid in a quantity sui'flcient to neutralize the catalyst, then addingwater until the material is precipitated and the inorganic salts formedare washed out. It is .during this step that I preferto subject thecellulose acetate to the action of a hypochlorite. The hypochloritesolution may be added to the secondary solution prior to the addition ofthe alkali carbonate or acetate, or the hypochlorite solution may beadded concurrently therewith. However, the hypochlorite solution shouldbe added before the addition of the large amount of water usedinprecipitating the cellulose acetate.

In like manner, the other organic esters and ethers of cellulose may besubjected to the hypochlorite treatment- Any suitable hypochlorite maybe employed in my invention, examples of which are the hypochlorites ofsodium, potassium, calcium or magnesium. The hypochlorite is appliedpreferably,

in an aqueous solution and of suitable concentration, and the time oftreatment is as required, say from 1 minute to 3 hours or more,depending on the concentration of the hypochlorite solution, therelative action of the same 'on the-cellulose derivative and thecondition of and chemicals contained in the primary solution of thecellulose derivative- In order to effect a rapid and high degree ofbleaching, the temperature of the treatment may be raised to above thatof room temperature, say from 24 to 100 0. However, this is notnecessary and successful results are obtained even at temperaturesbelow, room temperature.

Cellulose derivatives, having been treated with a hypochlorite solutionat the end of the ripening or hydrolysis period and then precipitated,may

' is emlnen tlysuitable for making clear plastics that have no pigmentsor dyes or for the making of light colored plastics. However, thederivative of cellulose produced by my process may be employed formaking dark' colored materials.

The derivative of cellulose, when treated by 7 my process, may be formedinto sheets and films by casting the same on film-forming wheels andbelts formed of metal alloys without corroding the same. Films formed ofa corrosive derivative of cellulose tend to take on a color or absorbthe discolored products of corrosion fromthe film-,casting belt orwheel. This property is obviated from the derivative of celluloseproduced in accordance with my invention, and a solution of suchderivatives of cellulose in a volatile solvent therefor may be spun intofilaments through spinning jets made of metal alloys with substantiallyno corrosive action on the spinning jets.

Thus, a cellulose derivative produced in accordance with my inventionforms more uniformed filaments, yarns, straws, etc. than those made ofuntreated derivatives of cellulose. The spinning into filaments oryarns-of an organic demay be less frequent and the replacing of jetssubstantially eliminated.

The derivatives of'cellulose treated in accordance with my invention mayalso be associated with volatile solvents therefor, and alsoplasticizers such as triacetin, diethyl tartrate, diButyl tartrate,diethyl phthalate, triphenyl phosphate,

etc. by any known processes, to form plastic sheets, blocks, tubes, rodsor articles by any suitable process. Another important application ofthis invention is in the making of molding powders containing a purifiedderivative of cellulose in finely divided condition in association withplasticizers but containing little or substantially no volatilesolvents; which molding powders may be molded under heat and pressure tothe desired shape. Films to be employed as a base for photographic orcinematographic films or forv other purposes may also be madefrom thismaterial. The purified derivative of" cellulose may also be used formaking lacquers,

particularly clear or light colored lacquers. The derivativesofcellulose made in accordance with this invention, being substantiallynon-corrosive,

are particularly suitable for use where solutions of the same involatile solvents are used to repeatedly or continuously contact withthe same 'metal surfaces.

Although it is preferable to treat the derivative of cellulose with thehypochlorite solution at or near the end of the hydrolysis or ripeningperiod, such solutions nevertheless may be treated with the hypochloritesolution immediately after esterification or etherification. Forinstance, cellulose acetate may be treated while in thechloroform-soluble state immediately after the cellulose has beenesterified by acetic anhydride and "Example I Cellulose acetateis'formedby the acetylation of cellulose with acetic anhydride in. the presenceof glacial acetic acid as a solvent and a suitable catalyst such assulphuric acid. The. solution formed after acetylation is allowed tostand'at a bility characteristics are obtained, a 20% aqueous solutionof sodium acetate is whipped into the solution to neutralize thesulphuric acid catalyst. The solution may then betreated by subjectingthe same to a solution of hypochlorite, the proportions as follows:

To every 100 parts (dry weight) of cellulose acetate dissolved in theacetic acid 'of the secondary solution there is added parts by weight ofa 12.1% aqueous solution of commercial calcium hypochlorite. Thehypochlorite solution is thoroughly whipped or stirred into thecellulose acetate solution. The cellulose acetate may then beprecipitated from the solution by j adding thereto, preferably whileconstantly agitating the same, a large quantity of water, for instance,800 parts by weight of water. Other methods of performing theprecipitation may be employed.

The cellulose acetate after the treatment with Y the hypochloritesolution and precipitation is tate.

separated from the mother liquor and the solution of hypochlorite iswashed from 1 to 5 or more times until free of chlorine and is thendried.

The cellulose acetate so treated in the fore going example has its colorgreatly reduced and its corrosive properties reduced substantially to aminimum.

Example II Example III The procedure of forming cellulose acetate is thesame as that described in Example I except that the solution of calciumhypochlorite is mixed with the aqueous solution of sodium acetate andthe solution containing the mixed salts added to the secondary solutionof cellulose ace- The cellulose acetate thus produced has substantiallythe same characteristics as those produced by the process of Example I.

. Example IV Cellulose acetate prepared by the process of Example I,1101' III may be treated while still wet from the precipitation andwashing steps with a bleaching agent preferably consisting of sodiumhypochlorite in the proportions as follows:

To every 100 lbs. of cellulose acetate figured on a dry basis, there isadded 0.36 gallon of. 3% available chlorine aqueous solution of sodiumhypochlorite in approximately 121.2 gallons of through orifices, itproduces a substantially uniform filament without effecting by corrosionthe diameter of the orifice.

solubility characteristics. After the desired solu- After any of theabove treatments containing a solution of a hypochlorite, the celluloseacetate may be given an anti-chlor treatment. For in stance, to every100 parts of cellulose acetate the same may be treated with .1 pound ofborax dissolved in 121.2 gallons of water. The anti-chlor treatment maybe effected on the cellulose acetate prior to precipitation in theprocesses described in Examples I to III inclusive. I

The derivatives of cellulose may be formed in any suitable manner andany suitable percentages of catalyst, reacting acid or alcohol andsolsolution employed will depend somewhat upon the amount of availablechlorine contained in the salt. Although the percentages, weights, etc.

given in the examples are preferred, a variation I of. 20% or more maybe made in either direction without departing from the spirit of myinvention. For instance, in Example I, instead of employing 5 parts byweight of a 12.1% aqueous solution of commercial calcium hypochlorite,there may be employed from less than 1'to 20 parts of the said solution,or the concentration of the solution may be modified.

It is to be understood that the foregoing de-. tailed description isgiven merely by way of. illustration and that many variations may bemade therein without departing from the spirit of my invention.

, Having described my invention, what I. desire to secure by LettersPatent is:

1. Method of reducing the corrosive action and otherwise improving theproperties of an organic derivative of cellulose comprising treating thesame while in the secondary solution with a solu-- tion capable ofliberating chlorine.

2. Method of reducing the corrosive action and otherwise improving theproperties of a derivative of cellulose comprising treating the samewhile in the secondary solution with a solution of hypochlorite.

.3. Method of reducing the corrosive action and otherwise improving theproperties of cellulose acetate comprising treating the same while inthe secondary solution with a solution of hypochlorite.

4. Method of. reducing the corrosive action and otherwise improving theproperties of an organic derivative of cellulose comprising treating thesame in its secondary solution and after hydrolysis with a solutioncapable of liberating chlorine.

5. Method of reducing the corrosive action and otherwise improving theproperties of a derivative of cellulose ,comprising treating the same inits secondary solution and after hydrolysis with a solution ofhypochlorite.

6. Method of reducing the corrosive action and otherwise improving theproperties of cellulose acetate comprising treating the same in itssecondary solution and after hydrolysis with a solution of hypochlorite.

'7. Method of reducing the corrosive action and 7/ otherwise improvingthe properties of. a deriva- I aroatoe l 9. Method of reducing thecorrosive action and otherwise improving the properties of an organicderivative of cellulose comprising treating the same while dissolved inthe secondary solution with a small amount of hypochlorite.

10. Method of. reducing the corrosive action and otherwise improving theproperties of cellulose acetate comprising treating the same whiledissolved in its secondary solution with 5%, based on the weight of thecellulose acetate, of a 12.1% 10 solution of calcium hypochlorite.

GEORGE SCHNEIDER.

